The Effects of Thermal Oxidation of a MEMS Resonator on Temperature Drift and Absolute Frequency

The dependency of the resonance frequency on temperature, in short temperature drift, of Si resonators is the major contributor to frequency inaccuracy of MEMS based oscillators. The temperature dependency can be reduced through thermal oxidation of the resonator (Melamud et al., 2007). However, in this paper it is concluded that thickness control of the oxidation layer has a major influence on the absolute frequency, besides on the temperature drift, and as such dominates the frequency spread of a MEMS resonator after production including oxidation. This is a result of the large difference in Young´s modulus of Si and SiO₂ and the added mass due to oxidation. The overall frequency range in operation - including both thermal drift range and spread in absolute frequency - can even deteriorate, rather than improve, through thermal oxidation, depending on the accuracy at which the oxide thickness is controlled.